Minimally invasive procedures are preferred over conventional techniques wherein the patient's body cavity is open to permit the surgeon's hands access to internal organs. Thus, there is a need for a highly controllable yet minimally sized system to facilitate imaging, diagnosis, and treatment of tissues which may lie deep within a patient, and which may be accessed via naturally-occurring pathways, such as blood vessels, other lumens, via surgically-created wounds of minimized size, or combinations thereof.
Currently known minimally invasive procedures for the treatment of cardiac, vascular, and other disease conditions use manually or robotically actuated instruments, which may be inserted transcutaneously into body spaces such as the thorax or peritoneum, transcutaneously or percutaneously into lumens such as the blood vessels, through natural orifices and/or lumens such as the mouth and/or upper gastrointestinal tract, etc. Manually and robotically-navigated interventional systems and devices, such as steerable catheters, are well suited for performing a variety of minimally invasive procedures. Manually-navigated catheters generally have one or more handles extending from their proximal end with which the operator may steer the pertinent instrument. Robotically-navigated catheters may have a proximal interface configured to interface with a catheter driver comprising, for example, one or more motors configured to induce navigation of the catheter in response to computer-based automation commands input by the operator at a master input device in the form of a work station.
In the field of electrophysiology, robotic catheter navigation systems, such as the Sensei® Robotic Catheter System (manufactured by Hansen Medical, Inc.), have helped clinicians gain more catheter control that accurately translates the clinician's hand motions at the workstation to the catheter inside the patient's heart, reduce overall procedures (which can last up to four hours), and reduce radiation exposure due to fluoroscopic imaging necessary to observe the catheter relative to the patient anatomy, and in the case of electrophysiology, within the relevant chamber in the heart. The Sensei® Robotic Catheter System employs a steerable outer catheter and a steerable inner electrophysiology (EP) catheter, which can be manually introduced into the patient's heart in a conventional manner. The outer and inner catheters are arranged in an “over the wire” telescoping arrangement that work together to advance through the tortuous anatomy of the patient. The outer catheter, often referred to as a guiding sheath, provides a steerable pathway for the inner catheter. Proximal adapters on the outer guide sheath and inner EP catheter can then be connected to the catheter driver, after which the distal ends of the outer sheath and inner EP catheter can be robotically manipulated in the heart chamber within six degrees of freedom (axial, roll, and pitch for each) via operation of the Sensei® Robotic Catheter System.
While the Sensei® Robotic Catheter System is quite useful in performing robotic manipulations at the operational site of the patient, it is desirable to employ robotic catheter systems capable of allowing a physician to access various target sites within the human vascular system. In contrast to the Sensei® Robotic Catheter System, which is designed to perform robotic manipulations within open space (i.e., within a chamber of the heart) after the outer guide sheath and inner catheter are manually delivered into the heart via a relatively non-tortuous anatomical route (e.g., via the vena cava), and therefore may be used in conjunction with sheaths and catheters that are both axially and laterally rigid, robotic catheter systems designed to facilitate access to the desired target sites in the human vascular system require simultaneous articulation of the distal tip with continued insertion or refraction of an outer guide sheath and an inner catheter. As such, the outer guide sheath and inner catheter should be laterally flexible, but axially rigid to resist the high axial loads being applied to articulate the outer guide sheath or inner catheter, in order to track through the tortuous anatomy of the patient. In this scenario, the inner catheter, sometimes called the leader catheter extends beyond the outer sheath and is used to control and bend a guide wire that runs all the way through the leader catheter in an over-the-wire configuration. The inner catheter also works in conjunction with the outer guide sheath and guide wire in a telescoping motion to inchworm the catheter system through the tortuous anatomy. Once the guide wire has been positioned beyond the target anatomical location, the leader catheter is usually removed so that a therapeutic device can be passed through the steerable sheath and manually operated.
Increasing the lateral flexibility of the sheath and catheter, however, introduces catheter navigation problems that may not otherwise occur when the sheath and catheter are laterally stiff. For example, many steerable catheters available today rely on the capability of the user to articulate the distal end of the catheter to a desired anatomical target. The predominant method for articulating the distal end of a catheter is to circumferentially space a multitude of free floating pullwires (e.g., four pullwires) into the wall of the catheter and attach them to a control ring embedded in the distal end of the catheter. The anchoring of each pullwire to the control ring is usually performed by soldering, welding, brazing, or gluing the pullwire to the control ring. If four pullwires are provided, the pullwires may be orthogonally spaced from each other. Each of these pullwires are offset from the center line of the catheter, and so when the wires are tensioned to steer the catheter tip, the resulting compressive forces cause the distal tip of the catheter to articulate in the direction of the pullwire that is tensioned. However, the compressive forces on the relatively flexible catheter shaft also cause undesired effects.
For example, the axial compression on the catheter shaft during a steering maneuver that bends the distal end of the catheter may cause undesired lateral deflection in the catheter shaft, thereby rendering the catheter mechanically unstable.
As another example, the curvature of the catheter shaft may make the articulation performance of the catheter unrepeatable and inconsistent. In particular, because the pullwires are offset from the neutral axis of the catheter shaft, bending the catheter shaft will tighten the pullwires on the outside of the curve, while slackening the pullwires on the inside of the curve. As a result, the amount of tension that should be applied to the pullwires in order to effect the desired articulation of the catheter distal end will vary in accordance with the amount of curvature that is already applied to the catheter.
As still another example, when bent, the articulate catheter distal end will tend to curve align with the catheter shaft. In particular, as shown in FIGS. 1A and 1B, operating or tensioning a pullwire on the outside edge of a bend may cause the catheter to rotate or twist as the pullwire may tend to rotate the distal articulating section of the catheter until the pullwire is at the inside edge of the bend. This rotation or twist phenomenon or occurrence is known as curve alignment.
That is, when the proximal shaft section of the catheter is curved (as it tracked through curved anatomy), and the distal section is required to be articulated in a direction that is not aligned with the curvature in the shaft, a wire on the outside of the bend is pulled, as shown in FIG. 1A. A torsional load (T) is applied to shaft as tension increases on the pull-wire on the outside of the bend. This torsional load rotates the shaft until the wire being pulled is on the inside of the bend, as shown in FIG. 1B. In effect, the tensioned wire on the outside of the bend will take the path of least resistance, which may often be to rotate the shaft to the inside of the bend rather than articulate the tip of the catheter adequately.
This un-intentional rotation of the shaft causes instability of the catheter tip and prevents the physician from being able to articulate the catheter tip in the direction shown in FIG. 1A. That is, no matter which direction the catheter tip is intended to be bent, it will ultimately bend in the direction of the proximal curve. The phenomenon is known as curve alignment because the wire that is under tension is putting a compressive force on both the proximal and distal sections and so both the proximal and distal curvature will attempt to align in order to achieve lowest energy state. The operator may attempt to roll the entire catheter from the proximal end in order to place the articulated distal tip in the desired direction. However, this will placed the tensioned inside pullwire to the outside of the proximal bend causing further tensioning of the pullwire, and possibly causing the distal end of the catheter to whip around.
All of these mechanical challenges contribute to the instability and poor control of the catheter tip, as well as increased catheter tracking forces. Some steerable catheters overcome these problems by increasing the axial stiffness of the entire catheter shaft (e.g., by varying wall thickness, material durometer, or changing braid configuration) or alternatively by incorporating axially stiff members within the catheter shaft to take the axial load. But these changes will also laterally stiffen the catheter shaft, thereby causing further difficulties in tracking the catheter through the vasculature of the patient. Therefore, the catheter designer is faced with having to make a compromise between articulation performance and shaft tracking performance. Other steerable catheters overcome this problem by using free floating coil pipes in the wall of the catheter to respectively housing the pullwires (as described in U.S. patent application Ser. No. 13/173,994, now issued as U.S. Pat. No. 8,827,948, entitled “Steerable Catheter”, which is expressly incorporated herein by reference), thereby isolating the articulation loads from the catheter shaft. However, the use of coil pipes adds to the cost of the catheter and takes up more space in the result, resulting in a thicker catheter wall. Furthermore, because the relatively stiff coil pipes are spaced away from the neutral axis of the catheter, its lateral stiffness may be unduly increased.
There, thus remains a need to provide a different means for minimizing the above-described mechanical challenges in a laterally flexible, but axially rigid, catheter.
Furthermore, although a single region of articulation is typically sufficient to allow a user to track and steer the catheter though the vasculature, it is sometimes inadequate for tortuous anatomies, navigation of larger vessels, or for providing stability during therapy deployment.
For example, it may be desirable to access either the right coronary artery or the left coronary artery from the aorta of the patient in order to remove a stenosis in the artery by, e.g., atherectomy, angioplasty, or drug delivery. The proximal curve of a catheter may be pre-shaped in a manner that locates the distal end of the catheter in an optimal orientation to access the ostium of the right coronary artery via the aorta, as shown in FIG. 2A. However, in the case where it is desirable to access the ostium of the left coronary artery, the proximal curve of the catheter locates the distal end of the catheter too far from the left coronary artery, which therefore cannot be easily accessed via manipulation of the distal end of the catheter, as shown in FIG. 2B. Alternatively, the proximal curve of a catheter may be pre-shaped in a manner that locates the distal end of the catheter in an optimal orientation to access the ostium of the left coronary artery via the aorta, as shown in FIG. 2C. However, in the case where it is desirable to access the ostium of the left coronary artery, the proximal curve of the catheter locates the distal end of the catheter too close to the right coronary artery, such that the distal end would be seated too deeply within the ostium of the right coronary artery, as shown in FIG. 2D. Thus, it can be appreciated that multiple catheters may have to be used to treat both the left coronary artery and right coronary artery, thereby increasing the cost and time for the procedure.
To complicate matters even further, the articulating distal end of the catheter needs to be long enough to cross the aorta from the patient right side to the left coronary artery. However, there are varying anatomies in the population with respect to the positioning of the left coronary artery in the aorta. For example, FIG. 3A illustrates the proximal curve required for a catheter to place the distal end within the ostium of the left coronary artery in a “normal” anatomy; FIG. 3B illustrates the proximal curve required for a catheter to place the distal end within the ostium of the left coronary artery in a “wide” anatomy; and FIG. 3C illustrates the proximal curve required for a catheter to place the distal end within the ostium of the left coronary artery in an “unfolded” anatomy. It can be appreciated that, even if is desired to only treat the left coronary artery, the clinician may have to be supplied with multiple catheters, one of which can only be used for the particular anatomy of the patient.
One way to address this problem in conventional catheters is to have multiple unique or independent regions of articulation in the catheter shaft by, e.g., adding a control ring and a set of pullwires for each articulation region. Thus, both a proximal region and a distal region of the catheter can be articulated. When manufacturing a catheter within only a single region of articulation, this task is not overly complex, typically requiring a single lamination of a polymer extrusion to form an outer jacket over an inner polymer tube (or liner) and the installation of the control ring with associated pullwires onto the assembly. A braided material can be installed between the inner polymer tube and outer polymer jacket to provide select region of the catheter with increased rigidity.
However, when manufacturing a catheter that has two regions of articulation, this task can be difficult and usually requires the lamination of an outer polymer jacket extrusion up to the proximal articulation region, then the installation of the most proximal control ring with attached pullwires, and then the lamination of an outer polymer jacket for the remaining portion of the catheter. For catheters with more than two regions of articulation, this process would have to be repeated for each and every additional region of articulation. Another issue with respect to the use of control rings is that the laminated polymer extrusion or extrusions need to be carefully sized at the control ring, since the ring itself consumes volume in the wall that not only requires thinner extrusions so as to not have a bulge in the catheter at the control ring, but also creates a significantly stiffer region the length of the control ring, which causes a “knuckle” where there should be a gradual stiffness change required to achieve good catheter performance during tracking through the vasculature.
There, thus, remains a need to provide a more efficient means for anchoring the distal ends of the pullwires at the articulating region or regions of a catheter.
As briefly mentioned above, the inner catheter and guide wire may be arranged in an “over-the-wire” configuration. However, such a configuration requires the guide wire to be at least twice as long as the inner catheter in order to allow the user to continuously hold the guide wire in place as the inner catheter is removed from the outer guide sheath. For example, the inner catheter can have a length up to 160 cm, with 140 cm of the catheter being inside the patient. Therefore, to ensure that the position of the guide wire is maintained, the physician will typically require a guide wire to be over 300 cm long. However, guide wires longer than 300 cm are not readily available in sterile catheter laboratories. Additionally, long guide wires require an extra assistant at the bedside to manage the guide wire and ensure it remains in a fixed position and always remains sterile. Furthermore, such a configuration disadvantageously increases the length of the robot required to axially displace the guide wire within the inner catheter to the fullest extent. The increased size of the robot may be impractical and too big and heavy to be mounted on a table in a catheter lab environment. Additionally, because the inner catheter passes entirely “over-the-wire,” the inner catheter cannot be robotically removed while holding the guide wire in place. Instead, the physician needs to remove the guide wire from the robot, and then slide the inner catheter proximally while holding the position of the guide wire fixed. The procedure time for removing the inner catheter from the outer guide sheath is increased for an over-the wire configuration (typically greater than one minute), thereby increasing fluoroscopic time and radiation exposure to the physician and staff.
A “rapid exchange” leader catheter would alleviate these concerns. Rapid exchange catheter designs have been described and documented in balloon angioplasty catheters, filters, and stent delivery system applications. These designs provide a rapid exchange port on the distal portion of the catheter shaft, which allows the guide wire to exit and run parallel to the proximal portion of the catheter shaft. However, no known designs exist for rapid exchange steerable catheters due to the challenge of navigating the pullwires proximal of the exit port. In addition, no known designs exist for the robotic interface for rapid exchange catheters.
There, thus, remains a need to provide the inner steerable catheter of a telescoping catheter assembly with a rapid exchange architecture.